In electrophotographic copiers, an image formed on the photosensitive drum is transferred to the copy paper by means of a transfer charger. Thereafter, the paper is separated from the drum by means of a well known corona charger used as a separation device. Japanese Laid-Open Patent Application Sho B 58-120282 discloses a scorotron charger used as the separation charger, the scorotron charger having a grid electrode interposed between a corona wire and the object to be charged, and which controls the amount of charge by controlling the voltage applied to the grid.